Various wireless transmission embodiments are known in the art. Some such systems support the transmission of voice data (comprising, in many instances, data that represents digitized voice), some the transmission of bearer data (comprising, for example, graphic information to be displayed or alphanumeric information as corresponds to an information file), and some support the transmission of both. An example of the latter are 802.11 compliant wireless local area networks (WLANs) that support the transmission of packetized digitized voice data (thereby implementing what is often referred to as voice-over-Internet-protocol or VoIP).
In some VoIP-facilitating WLAN systems, an access point to the WLAN will poll each and every extant subscriber unit then operating within the ambit of the access point on a regular basis. When a given subscriber unit responds to such a poll inquiry the access point will then transmit any previously received and buffered data (such as voice frames) as the access point may then have for that subscriber unit. This also constitutes an opportunity for the subscriber unit to transmit its own data, including voice data, if any to the access point. Such a protocol can be relatively effectively implemented to ensure that time-sensitive and even time-critical data (including voice data) is exchanged with sufficient speed and timeliness to ensure a generally acceptable level of quality of service. Unfortunately, however, such polling-based protocols also tend to require a considerable level of attentiveness on the part of the subscriber units. That is, the subscriber units must remain in a fairly constant state of reception in order to ensure that they do not miss their poll. As a result, subscriber units in such a system will tend to consume a considerable amount of power to maintain this state of activity. Such power consumption is ill-suited to the needs of portable devices, however, and particularly portable devices that only have a relatively limited portable power source.
As a partial answer to such a need, it has at least been proposed that the initiation of a new polling cycle occur in a regularly periodic and synchronized fashion. So configured, the subscriber units can know a priori when a new polling cycle will begin. After being polled (and transmitting and/or receiving such information as then requires attention) each subscriber unit can then in turn initiate a sleep mode of operation. Such sleep modes are well known in the art and permit a given device to effectively reduce power consumption by temporarily eliminating or at least reducing various power consuming tasks (such as receiving and processing transmissions from an access point). Sleeping subscriber units then switch to an active receiving mode of operation prior to the initiation of the next polling cycle. Such an approach can provide some power-saving benefits to at least some subscriber units. The benefits can be quite anecdotal, however, and the total savings in power consumption are sometimes not considered sufficiently adequate.
In other VoIP-facilitating WLAN systems, the access point and the subscriber units will all contend with one another for use of the available communication resource or resources. Such contention-based systems can be quite effective at facilitating a timely exchange of information in a fashion that leverages to considerable effect the available communication resource. Unfortunately, however, such contention-based protocols tend to be even more demanding of power consumption and availability. This results at least in part because the subscriber units must generally remain on at all times in order to avoid missing a transmission from the access point. Consequently, such contention-based protocols are relatively ill-suited for use with portable subscriber units having only limited power capacity.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are typically not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.